The neurotransmitter pathways within the inner plexiform layer (IPL) of the adult and developing retina will be investigated in the Old World monkey, Macaca fascicularis. In the adult retina, an immunocytochemical (Imcyt.) and autoradiographic (AR) analysis will be done to establish the morphological types of neurons utilizing GABA, glycine, substance P, somatostatin, acetylcholine and dopamine. The laminar pattern formed by the stratification of the process in IPL will be studied using qualitative and quantitative EM. The findings should provide a strong morphological and neurochemical basis for future work on the functional organization of IPL in primates. The developing retina will be examined in a series of fetal (F) eyes ranging in age between F70 and one year postnatal. The sequence of development of each neurotransmitter will be followed by means of quantitative EM, Imcyt and AR morphological methods, as well as neurochemical determination of neurotransmitter uptake, biosynthesis, release and receptor binding. This study will show the temporal properties of neurotransmitter genesis, and the ways in which morphological events during development correspond to these properties. It also will decide whether the laminar arrangement of IPL is stratified throughout development or whether the adult laminar pattern is developed from an initially diffuse pattern.